OSR: A Skill System

While building monsters for Kevin Crawford's excellent Silent Legions, I saw that a monster's save is 15 - HD (round up).  This inspired an idea for a skill system for early editions of DnD and the rest of the OSR.

Essentially, each Ability score will have an Ability Throw equal to 15 - 1/2 the Ability score (round down). To make an Ability Throw, simply roll equal to or above the Save.
E.G. Thaniel Dusk, a 3rd level Thief has a DEX of 13; his Ability Throw for DEX is 15 - 6 = 9.

I know that rolling under an ability score is very straightforward but, but I like that it is a roll high mechanic.